Api Key Exposure in Chi with Mongodb

Chi is a common server-side JavaScript runtime used for building APIs, and it often interacts with Mongodb to store and retrieve application data. When an API endpoint in a Chi application inadvertently exposes an API key — for example, by returning it in a JSON response or logging it in server-side output — the risk of credential leakage increases. This exposure can occur through verbose error messages, debug endpoints, or insufficient output filtering, especially when Mongodb documents containing sensitive keys are serialized and sent to clients.

Mongodb stores data in a flexible document format, and it is typical to persist configuration or integration keys alongside application data. If a Chi route queries Mongodb using user-supplied input without proper validation or authorization, an attacker may be able to manipulate the query to retrieve documents that include API keys. For example, an endpoint that builds a filter object directly from request parameters can allow an attacker to bypass intended access controls and extract sensitive fields.

In the context of middleBrick’s LLM/AI Security checks, this scenario is relevant because system prompt leakage patterns can inadvertently reveal stored API keys if responses from language models are improperly managed. Additionally, unsafe consumption of user input in Chi routes can lead to Server-Side Request Forgery (SSRF) or injection into Mongodb queries, further increasing the chance of key exposure. middleBrick’s checks for Input Validation, Property Authorization, and Data Detection help identify these risky patterns by correlating runtime behavior with OpenAPI specifications and known attack vectors such as those outlined in OWASP API Top 10.

An attacker might send a crafted request to a Chi endpoint to test for weak parameter handling, attempting to retrieve documents that should be restricted. If the application does not enforce strict schema validation or field-level permissions, the response could include database entries containing API keys used for external service authentication. This not only compromises the integrity of third-party integrations but may also enable lateral movement within infrastructure if keys are reused across services.

Using middleBrick’s CLI tool, you can scan a Chi endpoint that interacts with Mongodb to detect potential exposure of sensitive data. The scanner evaluates input handling, authorization logic, and output sanitization, highlighting findings that could lead to key leakage. For teams using the Pro plan, continuous monitoring can alert on new instances where API keys appear in responses or logs, helping to prevent accidental disclosure before it is exploited.

Remediation guidance centers around strict input validation, least-privilege access to Mongodb, and careful control of what data is returned by Chi routes. Avoid returning raw database documents to clients, and ensure that any keys stored in Mongodb are either encrypted or omitted from responses. By combining secure coding practices with automated scanning, you reduce the likelihood of API key exposure in applications built with Chi and backed by Mongodb.

To secure a Chi application that uses Mongodb, apply targeted fixes that prevent exposure of sensitive fields such as API keys. The following examples demonstrate safe patterns for querying, filtering, and returning data without leaking credentials.

1. Use Projection to Exclude Sensitive Fields

When retrieving documents from Mongodb, explicitly specify which fields to include in the response. This prevents API keys or other sensitive data from being sent to the client.

const { MongoClient } = require('mongodb');
const client = new MongoClient('mongodb://localhost:27017');

async function getUserPublicInfo(userId) {
  await client.connect();
  const db = client.db('myapp');
  const users = db.collection('users');
  // Only return safe fields, excluding apiKey
  const result = await users.findOne(
    { _id: userId },
    { projection: { name: 1, email: 1, apiKey: 0 } }
  );
  await client.close();
  return result;
}

2. Validate and Sanitize Input Before Querying

Ensure that user input used in query filters is validated and cannot be manipulated to access unauthorized documents. Avoid directly passing request parameters into Mongodb queries without constraints.

const Joi = require('joi');

const userQuerySchema = Joi.object({
  userId: Joi.string().hex().length(24).required()
});

async function safeGetUserRoute(req, res) {
  const { error, value } = userQuerySchema.validate(req.query);
  if (error) {
    return res.status(400).json({ error: 'Invalid input' });
  }

  const { MongoClient } = require('mongodb');
  const client = new MongoClient('mongodb://localhost:27017');
  await client.connect();
  const db = client.db('myapp');
  const users = db.collection('users');

  // Use validated input to construct safe query
  const user = await users.findOne({ _id: value.userId }, { projection: { apiKey: 0 } });
  await client.close();

  res.json(user);
}

3. Enforce Field-Level Security in Application Logic

Do not rely solely on database permissions; implement additional checks in Chi to ensure that a requesting user is authorized to view specific fields, especially when those fields contain API keys or secrets.

async function getSecureUserData(req, res) {
  const { userId, requestingUserId } = req.params;

  if (userId !== requestingUserId) {
    return res.status(403).json({ error: 'Forbidden' });
  }

  const { MongoClient } = require('mongodb');
  const client = new MongoClient('mongodb://localhost:27017');
  await client.connect();
  const db = client.db('myapp');
  const users = db.collection('users');

  const user = await users.findOne({ _id: userId }, { projection: { apiKey: 0 } });
  await client.close();

  res.json(user);
}

4. Rotate and Restrict API Key Usage

Even when keys are not exposed, minimize risk by configuring Mongodb and external services to accept only specific key formats or short lifetimes. Rotate keys regularly and audit their usage through access logs.

middleBrick’s CLI can be run regularly using middlebrick scan <url> to detect endpoints that may be returning sensitive fields. The GitHub Action can enforce that no build proceeds if findings related to key exposure are present, while the MCP Server allows developers to scan APIs directly from their coding environment in Chi.